Method of forming lithographic printing plate

ABSTRACT

LITHOGRAPHIC PRINTING PLATES ARE PREPARED FROM IMAGED SILVER HALIDE PHOTOGRAPHIC ELEMENTS BY CONTACTING THE ELEMENT WITH A BENZOTRIAZOLE SUBSTITUTED IN THE 4,5,6, AND/OR 7 POSITIONS. PORTIONS OF THE ELEMENT CONTAINING SILVER HALIDE ARE RENDERED OLEOPHILIC AND THUS RECEPTIVE TO OILY PRINTING INKS, WHILE PORTIONS FREE OF HALIDE ARE UNREACTIVE AND THUS OLEOPHOBIC.

United States Patent Office 3,764,323 Patented Oct. 9, 1973 signors to APECO Corporation, Evanston, Ill. No Drawing. Filed Apr. 15, 1971, Ser. No. 134,399

Int. Cl. G03f 7/ 02 US. CI. 96-33 8 Claims ABSTRACT OF THE DISCLOSURE Lithographic printing plates are prepared from imaged silver halide photographic elements by contacting the element with a benzotriazole substituted in the 4, 5, 6, and/ or 7 positions. Portions of the element containing silver halide are rendered oleophilic and thus receptive to oily printing inks, while portions free of halide are unreactive and thus oleophobic.

This invention relates to lithographic printing, and more particularly concerns the provision of a lithographic printing plate from an imaged photographic emulsioncoated element. Otherwise stated, the invention concerns the conversion of a silver halide photographic image to an oleophilic, or oil-receptive, lithographic printing plate.

In the art of photolithography, a photographic image is converted into a medium that is receptive to oily or greasy inks. Desired objectives of methods for effecting this conversion include: a method which is simple, rapid, convenient, and low in cost; reagents which are readily prepared and are stable and consistent in use; lithographic printing plates which may be stored for long periods, either wet or dry, and in the presence of comparatively strong light; and a method which permits a positive printing plate to be made directly from a photographic negative.

Additionally, while it is presently conventional to develop the emulsion before converting it to an oleophilic plate, proposals have been made for simultaneously conducting the developing and conversion in a monobath solution. An additional objective is to provide a conversion reagent suitable for conversion after developing, or for conversion simultaneous with developing.

In accordance with the invention, we have now discovered that imaged silver halide photographic elements, or layers, may be converted to lithographic plates of outstanding quality by contacting the elements with certain benzotriazole derivatives, that is, one or more benzotriazoles substituted in the 4, 5, 6, and/or 7 positions, and having the formula:

The substituents may be any functional groups that do not react adversely with components of the conversion reagent, and may, for example, be alkyl, 'aryl (including fused ring), halo, nitro, amino, nitroso, hydroxy, alkoxy, etc., and combinations thereof. The process of the invention converts silver halide to an oleophilic ink-receptive medium, and in all respects meet the desired objectives above.

As normally employed, the reagents of the invention are applied to a negative silver halide photographic element which has been developed by the action of a conventional developer, or reducing agent, and which has not been treated with a fixing solution. Developing converts exposed portions of silver halide to metallic silver, which is not reactive with the benzotriazole reagent, while retaining unexposed silver halide in the element. The metallic silver remains oleophobic and hydrophilic.

Alternatively, a printing plate may be prepared directly from an imaged but undeveloped photographic element. For this embodiment the element is simultaneously developed and converted to an oleophilic medium by treatment in a monobath containing both a developer and the conversion. reagent. In monobath processing, however, the conversion reagent should be replenished or replaced more frequently than in multibath processing.

The reagents of the invention may be used with many of the common silver halide photographic elements, preferably those in which the halide is chloride, alone or with additional amounts of bromide and/or iodide. As will be apparent from the examples below, the silver halidegelatin emulsion may be applied onto a suitable photographic base, whether transparent, translucent or opaque. These bases are usually subbed or otherwise treated to make them accept an aqueous emulsion, as known in the art.

Treatment of the developed photographic element with a benzotriazole derivative reagent of the invention is conveniently elfected in an aqueous alkaline medium. Optimum reagent concentrations have been determined for S-chlorobenzotriazole, and presumably are within i50% of these values for other benzotriazoles. Reagent concentrations (for 5-chlorobenzotriazole) on the order of about 0.25 to 2.5 grams per liter, e.g. 1.0, appear optimal, with concentration higher than about 5 g./l. being unnecessarily concentrated, while concentrations below about 0.25 occasionally failing to produce good prints. Simple tests, as set forth below, provide corresponding information for other derivatives. The alkali concentration (for S-chlorobenzotriazole) is advantageously about 1% by weight, and may range from less than 0.1% to more than about 4% sodium or potassium hydroxide.

If desired, a portion of the hydroxide may be replaced with an alkaline salt such as the carbonate. When the alkali concentration exceeds about 2%, the addition of colloidal gold appears to be of advantage, although there is no clear explanation for this phenomenon.

The conversion reagent may include wetting agents such as the non-ionic detergents; gelatin hardening agents such as sodium sulfate and sodium and/or chromic acetate; water soluble polymers; and other materials found useful for maintaining a clean print background.

A wide variety of benzotriazole derivatives may be used for the invention. The substituted benzotriazoles include the preferred 5-chloro, the satisfactory S-methyl, 5,6-dimethyl, and 4,5-dichloro, and the somewhat less effective 5-nitr0 compounds. The 4-amino, 6-amino, o-dimethylamino, 6-hydroxy, and other derivatives may also be used as required. Unsubstituted benzotriazole is unsatisfactory.

The benzotriazole derivatives of the invention may be shipped and stored either as the solid products, the solid products mixed with an anhydrous alkali such as sodium or potassium hydroxide, or in aqueous solution either with or without the alkali. Alkalies are helpful in dissolving the derivatives. Wetting agents, hardening agents, water soluble polymers, and other materials may, if desired, be included in the solid products or in concentrates.

The invention and various aspects thereof are exemplified in the following operating examples, which are intended to be illustrative of the invention without necessarily being exclusive or wholly definitive.

EXAMPLE I In this example a silver chloride photographic element is converted to a printing plate by the action of 5-chlorobenzotriazole.

Typically, a contrasty silver chloride emulsion is coated on a photographic paper base to a coating weight of about 5.8 grams of liquid emulsion per 'squ'afefoot'The silver content of the emulsion is equivalent to 30 grams Water to make 1000 ml. at room temperature.

Fair-mount. 2 Harleco, #2396.

The solution is green in color; specific gravity (22 C): 1.002; pH (22 C.)-=10.8.

After developing, the element is squeegeed, contacted with the converting reagent at 70 F. for about 20-3O seconds, squeegeed dried, and etched by swabbing with a suitable starting solution, e.g. APECO Starting Solution before use.

Printing is with a Multilith A/M #1250 offset duplicator press, using ink (A/M, black ml-pd #304), and as fountain, APECO Starting Solution diluted 1:7 with water. At least 1000 good prints were obtained in 50 pound paper stock.

EXAMPLES II, III, IV

These examples illustrate the preparation of lithographic printing plates from a variety of benzotriazole derivatives, namely the S-chloro, the S-methyl, and the 5,6-dimethy1 benzotriazole.

The procedure followed is essentially that of Example I, except that the converting reagent in each case is prepared as follows:

Water ml 500.0 CH COONtl, anhyd. g.. 10.0 (CH COO) CI"H O g 1.0 [Benzotriazole deriv.] g 0.5 CH OH ml 20.0 Colloidal gold ml 5.0 'NaOH ..g 20.0 Water to make 1000.0 ml. at 70 F.

I Results are as follows:

Rating Example Benzotriazole Print No. 1 Print No. 100

II".- fi-chloro Excellent Excellent. 111---; 5-methyl. Fair-poor"-.- Good. IV 5,6 diruethyL- Fair-good Fair.

Unsubstituted- None- EXAMPLES V, VI, VII, VIII, IX

In these examples the efiect of various 5-chlorobenzotri zole oncentrations is determined.

Theprocedure follows that of Exatnples' H through-IV, except that the NaOH is reducedto 15.0 g.; and that 5-chlorobenzotriazole is used in each case.Its concentration is varied as shown. The following results are obtained:

Concentration,

Example Print- No. 1 PrintN'ofifOO 0 Fail Fail 0. 10 Poor-fair- O. 25 Fair. 0. 50 0.75 .do Do. 1. 00 Excellent s Excellent.

As an illustration of the stability of the present [coinverting reagents, 2 /2 gallons of the reagent ofEX mPl e VII has been found satisfactory for the processing] of more than 1,000 10 x 15" photographic emulsioii'plates'. Other experiments similar to those of the eaiamplbs above establish the previously indicated NaOH 'conceh' tration preference. Also, a sodiurnacetate concentration of between 4 and 12 g./l. is demonstrated to be optimum. Monobath solutions for concurrent developing'and converting may be prepared by mixing equal volumes .of developer and converting reagent as set forth above,e.g; in Example I. Because of interaction between the two solutions, it is desirable that they be mixed shortly before use. u Y

For some purposes it is desirable to incorporate the converting reagent in the photographic elementQAccord ingly, the benzotriazole is then incorporated" onto the element itself, advantageously in a gelatin emulsion layer adjacent the silver halide-containing layer. Immersionin an alkaline developer thereby activates the benzotriazole. and simultaneously develops the image and renders it oleophilic. I While the invention has been illustrated by various em bodiments thereof, it is evident many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all'such alternatives; modifications and variations which fall within the spirit and broad scope of the appended claims." We claim as our invention: 1. A method of forming a; lithographic printing plate from an imaged silver halide photographic element having portions containing silver halide and portions*free of silver halide which comprises: contacting said element, while in an aqueous alkaline environment providing an alkalinity equivalent to about 0.01%to 4% of sodiun'fo'r potassium hydroxide, with a benzotriazolesubstitutedat least one of the 4, 5, and 6 positions-with-a substitue-nt selected from the group methyLchloro and combinations thereof, in a concentration equivalent to from about 0.25

- to about 2.5 grams of said benzotriazole per liter, and in an amount suflicient to produce acceptable quality prints when said printing plate is subsequently treated with an oleophilic printing ink, to thereby convertv said portions containing said silver halide to an oleophlicink-receptive medium. v

2. Method of claim 1 including the step, prior to sa d contacting, of developing said element. M I n v 3. Method of claim 1 wherein said element is simul} taneously treated with amonobath containing developer and said benzotriazole. 4. Method of claim 1 wherein said benzotriazole is 5-chlorobenzotriazole. w 5. Method of claim 1 where said benzotriazole is S-methylbenZotriazole. 6. Method of claim 1 wherein "said benzotriazole is. ,6-dime hylbenzotriazole. a

5 6 7. Method of claim 1 wherein said benzotriazole is in 3,454,398 7/1969 Wendt 96-29 L X an aqueous alkaline solution. 3,490,906 1/1970 Blake 9629 L 8. Method of claim 7 wherein said solution contains colloidal gold When the alkali concentration is in excess OTHER REFERENCES of about 2%.

Patterson, A. M., et al.: The Ring Index, 2nd ed., 1966,

References Cited American Chemical Society, pp. 146 and 152 only.

UNITED STATES PATENTS DAVID KLEIN, Primary Examiner 3,511,656 5/1970 Regan et al 9633 X 3,390,993 7/1968 C016 9666.5 10 US 3,146,104 8/1964 Yackelet a1. 9633 96 29- L; 101-466 

